imponer

to impose, impressirregular-er verb

Where it breaks the pattern

imponer follows poner: irregular first-person form
imponer follows poner: irregular preterite stem; the 1s and 3s endings are unstressed, so they carry no written accent
imponer follows poner: irregular future stem; the endings themselves are regular
imponer follows poner: conditional shares the irregular future stem
imponer follows poner: present subjunctive is built from the irregular yo form
imponer follows poner: imperfect subjunctive is built from the third-person preterite stem
irregular past participle

Indicativo: imponer conjugation

	Presente	Pretérito	Imperfecto	Futuro	Condicional
yo	impongo	impuse	imponía	impondré	impondría
tú	impones	impusiste	imponías	impondrás	impondrías
él / ella / Ud.	impone	impuso	imponía	impondrá	impondría
nosotros	imponemos	impusimos	imponíamos	impondremos	impondríamos
vosotros	imponéis	impusisteis	imponíais	impondréis	impondríais
ellos / Uds.	imponen	impusieron	imponían	impondrán	impondrían

Participio: impuesto · Gerundio: imponiendo

irregular form

Real sentences with the conjugated form highlighted, from Tatoeba, licensed under CC BY 2.0 FR.

Se impuso un impuesto especial a los coches importados.
A special tax was imposed on imported cars.
Las localidades impusieron prohibiciones al desarrollo.
Localities imposed bans on development.
Tom se impuso a Mary.
Tom overpowered Mary.

These verbs are poner with a prefix, and they inherit its irregular forms.